1) Field
The embodiment relates to an optical semiconductor device.
2) Description of the Related Art
In recent years, together with downsizing and reduction of power consumption of a module for optical communication, an optical device which can operate also at a high temperature such as a semiconductor laser, an optical modulator or the like is demanded.
Mainly, an InGaAsP-based material has been and is being used for an optical device used for an optical fiber communication system.
Recently, development of an optical device for which an AlGaInAs-based material is used and which can implement sufficient high-speed operation at a high temperature due to the superior band structure of a hetero-junction is advancing.
Further, an optical device having a buried heterostructure attracts attention because driving current can be reduced and speedup can be anticipated thereby.
Here, FIG. 5 shows a configuration of a conventional buried-type (buried-heterostructure) semiconductor laser (optical semiconductor device) made from an AlGaInAs-based semiconductor material.
As shown in FIG. 5, the conventional AlGaInAs-based buried-heterostructure semiconductor laser has a structure (pnpn current blocking structure) formed in such a manner that an n-side AlGaInAs optical guide layer 101, an AlGaInAs/AlGaInAs strained multiple quantum well (MQW; Multiple Quantum Well) active layer 102, a p-side AlGaInAs optical guide layer 103, a part of p-type InP cladding layer 104 are stacked in order on an n-type InP substrate 100, when necessary, with an InP buffer layer (not shown) interposed therebetween, and the stacked structure is processed into a mesa shape and buried with a p-type InP burying layer and an n-type InP burying layer (pn burying layer 106), then a part of p-type InP cladding layer 104 and a p-type InGaAs contact layer 105 are formed.
Also semiconductor lasers having other waveguide structures such as other buried heterostructures wherein the mesa-shaped structure is buried with a high-resistance semiconductor layer (semi-insulating buried heterostructure; SI—BH structure) or a ridge structure are available.
In a buried-heterostructure semiconductor laser having such an AlGaInAs-based multiple quantum well active layer as described above, since a quantum well on the conduction band side for electrons whose effective mass is small is deep and a quantum well on the valence band side for holes whose effective mass is large is shallow, the temperature dependence of the current-light output characteristic is small. Further, since the semiconductor laser has the buried structure, the relaxation oscillation frequency is high.
On the other hand, if an electric field absorption type modulator is configured so as to include an AlGaInAs-based multiple quantum well active layer, then a steep extinction characteristic with respect to the voltage is obtained.
It is to be noted that Japanese Patent Laid-Open No. 9-36494 and Japanese Patent Laid-Open No. 2002-26457 have been found as a result of research for the prior art.